1. Field of the Invention
The present invention relates to parity detection in a CDMA mobile communications system, specifically, to a parity detection device and method in a CDMA mobile communications system, which detects parity error in data output from a cell site modem (Q51601-2S1), and controls the data output when the parity error occurs, to improve the reliability in data communication.
2. Discussion of Related Art
In a CDMA mobile communications system, which conforms to a protocol defined in calling process of Electronic Industrial Association, a mobile, which is in the initial state with the power application, searches the control channel of a base station (cell site) which sends the highest intensity of signal, that is, the nearest base station at the location where the mobile is currently placed. When the mobile searches the nearest control channel, it goes to hook-on mode, and receives a message that the current base station transmits through a selected channel. The base station performs communications about the entire mobile communications through a communication message, which is transmitted/received between the base station and mobile, or base station and control unit, other than the aforementioned message. Here, a cell cite modem (CSM) is used. That is, data is transmitted and received through the CSM in the data communications between the base station and mobile, or base station and control unit.
FIG. 1 shows the configuration of the CSM. Referring to FIG. 1, the modem includes a base station modulation section 1 having a plurality of modulators 1a to 1d which modulate four channels of data to be transmitted, and first, second and third data combining sections 2, 3 and 4 for combining the channel data modulated by each of modulators 1a to 1d of base station modulation unit 1 by alpha, beta and gamma sectors.
In the modem constructed as above, which is applied to the base station of a conventional CDMA mobile communications system, each of modulators 1a to 1d in base station modulation section 1 modulates data to be transmitted for each sector (alpha, beta and gamma) into 9-bit parallel data in the form of 2's complement, to which I and Q signals are added. The modulated data of the four channels, which are output from the modem, becomes four pieces of sector data for each sector. The four pieces of sector data are selectively applied to first, second and third data combining sections 2, 3 and 4, processed therein, and transmitted through a transmitter (not shown).
The data combining sections are described below in detail. With first data combining section 2 having four channels, first to four signal separators 2a to 2d separate the I and Q signals from the alpha data of four channels, and first to four adders 2e to 2h add the separated I and Q signals in the unit of two I signals and two Q signals. The added I signals are added once again by a fifth adder 2i, and transmitted as 10-bit channel data to the transmitter. The added Q signals are added again in a sixth adder 2j, and transmitted as 10-bit Q-signal channel data to the transmitter.
The configuration and operation of second and third data combining sections 3 and 4 are identical to those of first data combining section 2, so that the explanation for the second and third data combining sections will be omitted. However, different from the first data combining section, the second data combining section processes the modulated beta data, and the third data combining section processes the modulated gamma data.
The above-described CSM of the conventional CDMA mobile communications system can be realized without a separate serial/parallel converter because the channel data output from each base station modulator in base station modulation unit 1 is 9-bit parallel data. However, the 9-bit parallel data has no parity bit for checking if there is data error, so that parity check is impossible. Thus, the reliability of data cannot be secured. Furthermore, one modulator and one digital adder are required for one channel in the conventional CSM. This means that the number of modulator and digital adder increases when the communications system needs a lot of channels. This complicates the configuration of the system.
To solve this problem, a CSM 5 shown in FIG. 2 has been developed. This modem is constructed in a manner that the plurality of modulators and adders of FIG. 1 are built in one chip. The output of the modem is 16-bit two bit streams of serial data where I and Q signals of the three sectors (alpha, beta and gamma) are separated from each another. This data consists of 15-bit serial data in 2's complement, and one parity bit.
While CSM 5 can reduce the size of the system, compared to the modem of FIG. 1, data communication is performed without detection and correction of error in the data which is outputted from the base station even though there is the parity bit for correcting the error of output data. Thus, reliability in data communications cannot be secured. In other words, even when error occurs in data output from the CSM, the data having error is transmitted to a mobile or control unit, resulting in malfunction of them.